Expected Consequences of a 4 Degrees Celsius Global Temperature Rise
Venice is already in danger of sinking beneath the waves and the peril will increase as sea levels rise. Photograph: Franco Debernardi/Getty Images
By Alister Doyle, Reuters
World temperatures could soar by 4 degrees Celsius (7.2 degrees Fahrenheit) by the 2060s in the worst case of global climate change and require an annual investment of $270 billion just to contain rising sea levels, studies suggested on Sunday.
Such a rapid rise, within the lifetimes of many young people today, is double the 2 degrees C (3.6 degrees Fahrenheit) ceiling set by 140 governments at a U.N. climate summit in Copenhagen last year and would disrupt food and water supplies in many parts of the globe.
Rising greenhouse gas emissions this decade meant the 2 degree goal was “extremely difficult, arguably impossible, raising the likelihood of global temperature rises of 3 or 4 degrees C within this century,” an international team wrote.
The studies, published to coincide with annual U.N. climate talks in Mexico starting on Monday, said few researchers had examined in detail the possible impact of a 4 degrees C rise above pre-industrial levels.
“Across many sectors, coastal cities, farming, water stress, ecosystems or migration, the impacts will be greater,” than at 2 degrees, wrote Mark New of Oxford University in England, who led the international team.
One study, published in the British journal Philosophical Transactions of the Royal Society A, said temperatures could rise by 4 degrees C in the worst case by the early 2060s.
Other scenarios showed the threshold breached later in the century or not at all by 2100, raising risks of abrupt changes such as a loss of Arctic sea ice in summer, a thaw in permafrost or a drying out of the Amazon rainforest.
One of the papers gave what it called a “pragmatic estimate” that sea levels might rise by between 0.5 and 2 meters (1.64 to 6.56 feet) by 2100 if temperatures rose 4 degrees Celsius.
Containing a sea level rise of 2 meters, mostly building Dutch-style sea walls, would require annual investments of up to $270 billion a year by 2100.
That sum might limit migration to perhaps 305,000 people from the most vulnerable areas, wrote Robert Nicholls of the University of Southampton. Lack of protective measures could mean the forced resettlement of 187 million people.
People living on small islands, in Asia, Africa or river deltas were most at risk.
The studies concluded that governments should do more both to cut greenhouse gas emissions and research back-up methods such as “geo-engineering” programs that could dim sunlight or seek to suck greenhouse gases from the air.
Four Degrees and Beyond: The challenges of a world warmed by 2 or 4 degrees, UN Climate Change Convention, Opening Report
By Robin McKie
Oxford scientists have contributed to a series of research papers about the impacts of global warming to coincide with the opening of the Climate Change Conference in Cancun, Mexico.
Devastating changes to sea levels, rainfall, water supplies, weather systems and crop yields are increasingly likely before the end of the century, scientists warn.
A special report, released at the start of climate negotiations in Cancún, Mexico, will reveal that up to a billion people face losing their homes in the next 90 years because of failures to agree curbs on carbon emissions.Up to three billion people could lose access to clean water supplies because global temperatures cannot now be stopped from rising by 4C.
“The main message is that the closer we get to a four-degree rise, the harder it will be to deal with the consequences,” said Dr Mark New, a climate expert at Oxford University, who organised a recent conference entitled “Four Degrees and Beyond” on behalf of the Tyndall Centre for Climate Change Research.
The papers are in a special report ‘Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications” published today in Philosophical Transactions of the Royal Society A.
A key feature of these papers is that they assume that even if global carbon emission curbs were to be agreed in the future, these would be insufficient to limit global temperature rises to 2C this century – the maximum temperature rise agreed by politicians as acceptable. “To have a realistic chance of doing that, the world would have to get carbon emissions to peak within 15 years and then follow this up with a massive decarbonisation of society,” said Dr Chris Huntingford, of the Centre for Ecology and Hydrology in Oxfordshire.
Few experts believe this is a remotely practical proposition, particularly in the wake of the failure of the Copenhagen climate talks last December, a point stressed by Bob Watson, former head of the Intergovernmental Panel on Climate Change and now chief scientist at the Department for Environment, Food and Rural Affairs. As he put it: “Two degrees is now a wishful dream.”
Researchers such as Richard Betts, head of climate impacts at the Met Office, calculate that a 4C rise could occur in less than 50 years, with melting of ice sheets and rising sea levels.
According to François Gemenne, of the Institute for Sustainable Development and International Relations in Paris, this could lead to the creation of “ghost states” whose governments-in-exile would rule over scattered citizens and land lost to rising seas.
Small island states such as Tuvalu and the Maldives are already threatened by inundation. “What would happen if a state was to physically disappear but people want to keep their nationalities?” he asked. “It could continue as a virtual state even though it is a rock under the ocean.”
Peter Stott of the Met Office said the most severe effect of all these changes is likely to involve changes to the planet’s ability to soak up carbon dioxide. At present, around 50% of man-made carbon emissions are absorbed by the sea and by plants on land.
“However, the amount of carbon dioxide that can be absorbed decreases as temperatures rise. We will reach a tipping point from which temperatures will go up even faster. The world will then start to look very different.”